TRENTON — Senate President Stephen Sweeney’s push to stiffen the state’s gun laws got off to a rocky start today as the Assembly majority leader warned the package of measures was dead on arrival because it wasn’t tough enough, and a national group of mayors abruptly put off its endorsement.

The organization, Mayors Against Illegal Guns, had planned to endorse Sweeney’s package of bills at a news conference Friday in Atlantic City, but balked because of a provision that would extend the life of handgun purchase permits from 90 days to four years, The Star-Ledger learned.

Not long afterward, Assembly Majority Leader Lou Greenwald (D-Camden) warned that the bills proposed by his fellow South Jersey Democrat would not even be considered because they lacked a provision to reduce the size of magazine clips from 15 bullets to 10.

"Let me be crystal clear: As majority leader, I would not advocate moving any gun violence-prevention package unless a ban on high-capacity magazines is included," said Greenwald, whose chamber has already passed its own package of measures that is tougher than the Senate version.

Greenwald said today he was confident the Assembly and Senate Democrats could reach a compromise, but he made it clear that it must include clip limits.

"Without it, it’s not meaningful reform," he said. "We are not going to consider a package of bills unless there is meaningful reform."

Sweeney’s staff declined to address Greenwald’s concerns, but the Senate president has often ignored the Assembly’s wishes.

Last week, Christie unveiled a package of gun measures that would strengthen background checks, make it easier to commit the mentally ill, require parental consent when minors purchase the most violent video games and impose stiffer sentences on criminals.

New Jersey already bans assault weapons, requires a seven-day waiting period before buying a handgun and limits purchases to one a month. But the shooting deaths of 20 first-graders in Connecticut in December set off a national wave of introspection and efforts to stiffen gun laws.

The centerpiece of the New Jersey Senate plan would create an electronic system for instant background checks for the sale and transfer of firearms, including a photo ID for purchases. This would allow for real-time reporting and would attempt to immediately identify those barred from buying firearms.

"By using common sense and new innovative technologies, we can build upon New Jersey’s already stringent gun laws and help reduce gun violence in our state," Sweeney said in a statement introducing the bills.

The package also requires the immediate loss of gun permits at criminal sentencings and for residents who are involuntarily committed.

Other measures in the package include a ban on the Barrett .50 caliber rifle, a crackdown on straw purchases and upgrading penalties for illegal trafficking.

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But Assembly resistance was not the only setback for Sweeney. Mayors Against Illegal Guns, founded and headed by Mayor Michael Bloomberg of New York, alerted backers of Sweeney’s proposals by e-mail today that it was postponing the endorsement after learning of the provision that would extend the life of handgun purchase permits.

Brian Levinson, the coalition coordinator, said in the e-mail obtained by The Star-Ledger that law enforcement authorities feared the change would hinder timely background checks,

"Based on conversations we’ve had with several police chiefs around the state, we believe this provision would make it more difficult for law enforcement to keep guns out of dangerous hands," Levison said.

But Chris Donnelly, a spokesman for Sweeney (D-Gloucester), said the new law would create a stronger system of checks that would allow for the expanded permit time. He said residents would have to obtain a permit, then swipe an ID card and go through an instant background check at the point of sale.

"Police departments will still have the ability to deny individuals they feel should not be in possession of a gun. … The new system will make this process more efficient," Donnelly said.

The organization also said it had concerns about whether the Senate package increased the number of handguns a resident could buy at one time, although Donnelly said they would still be able to buy only one a month.